The venous system includes a multitude of one-way bicuspid valves that permit substantially unidirectional blood to flow toward the heart. These valves are particularly important in the lower extremities to prevent the pooling of blood. When the leaflets of the bicuspid valves fail to close properly, the valve is considered “incompetent” as it permits leakage of retrograde flow resulting in the abatement of flow towards the heart.
This potentially serious condition is known as “chronic venous insufficiency.” Symptoms can progress from unsightly “spider” or varicose veins to skin discoloration and painful skin ulcerations. The etiology of venous insufficiency is multifactorial, including a past history of thrombotic events, chronic venous stasis, and venous hypertension. Current treatments for venous insufficiency include elevation of the feet and compression stockings. While these can relieve symptoms, the underlying disease remains untreated. Surgical techniques are also employed in which native valves can be bypassed or replaced with autologous sections of veins having functioning valves.
Minimally invasive techniques and instruments for placement of intraluminal medical devices have been developed to treat and repair undesirable conditions within body vessels, including treatment of conditions that affect blood flow such as venous insufficiency. Recently, prosthetic valves implantable via intraluminal transcatheter delivery systems have been developed. However, post-implantation thrombosis and platelet deposition on surfaces of endovascular prosthetic valves may occlude the conduit defined by the endovascular prosthesis or compromise the function of an implanted valve by limiting the motion or responsiveness of moveable portions of the device such as valve leaflets.
To prevent such occlusion, prosthetic valves may be implanted in combination with therapeutic agents. For example, a therapeutic agent may be locally administered through a catheter positioned within the body vessel near the prosthesis, or by coating the prosthesis with the therapeutic agent. Unfortunately, such methods and coated prostheses have not been completely effective in preventing impaired valve function due to the short time interval over which the therapeutic agent is delivered to the site of implantation.